setting out slates ,advice needeed

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hi there
im about to start my new roof next week and need a bit of advice on setting out the slates
im using marley melbourne interlocking slates and need to know if the slates on the main roof should line up with the slates on an intersecting roof which is slightly lower, do i simply do the standard battern gauge calculation for each roof and be done with it or do i try and make the guage on the taller roof match the one of the smaller roof, even if it means the top slate having a larger overlap
i hope this makes sence
ive included a few pics to try and explain what i mean
in the pic attched, that i found on this forum
the slate on each roof do not line up, is this normal?

cheers
jon
 
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Treat each roof area separately, don't try to line up the courses.

Work out the number of courses required and set the battens so that they are all at the same gauge, that will ensure that the finished roof looks 'right'
 
cheers roofer, this advice is music to my ears as ive been stressing about this dilema all week
i have one other question

the GRP Slate dry valley system get deliverd tomorow and im just researching on how to fit it, i get the basics but am a bit confused on fitting
the valley boards, i understand that they have to sit flush with the top of the rafters so that they do not kick up the slate at the valley edge
but what i dont get is on the marley sitework guide it says

"In all cases valley boards should be fitted. Valley
boards may be inset or continuous over the
rafters. Where they are inset, they should be a
maximum of 12mm thick and supported on
bearers or noggings of 50 x 25mm or similar
and set at a depth to suit the thickness of the
Valley Board"

i dont get why they have to be a maximum of 12 thick, is this a misstake, as surley being thicker than 12mm makes no difference?
my roof timbers are 6x2 , is it not possible for me to nog the gaps down the valley with 6x2 intead so that the are flush with the rafters

cheers again

jon
 
I agree with you, I think that must be a typo and should read 'minimum' 12mm.

With GRP valleys, the valley boards are a bit of an overkill, provided the troughs are well supported then noggins between the rafter are suitable.

Make sure you also have noggins to support the batten ends as well.
 
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Just finished two 7 mt valleys using GRP troughs, no probs.
Now come to trying to use the same GRP troughs on four short valleys on two dormers that discharge halfway down the pitch of the main roof.
Does anyone know how you dress the bottom of the valley onto the slates bearing in mind that the troughs sit on battens which are fixed to the valley boards , these battens ending up on the same plain as the main slate battens which means the bottom of the "V" of the trough being the thickness of the batten lower is going to discharge under the slates they are supposed to discharge onto. Been onto the manufacturers and they have no details of the troughs used in any other situation other that a normal valley dicharging into a gutter.
Am I missing something or are you suposed to dress the bottom of the valley with a leaded step onto the slates which seems to defeat the object to me and is going to form a water/ice trap. Any help anyone and thank you in anticipation.
 
GRP valleys are a pain on mid slope dormers as you need a large lead saddle to get the water away, by the time you add in the top saddle it is just as cost effective to use lead anyway.
 
They dont line up because they are slates and not interlocking tiles.
The slate would likely have been pre holed for 100mm head lap. So the gauge is set in stone so to speak.

There are different fascia hieghts so rafter lengths are not the same. hence slates dont line up pefectly.. not a bad job though..

You can adjust your interlocking tiles gauge within limits to try and get them to course.

Dormer valley as SRE says use a lead saddle
 

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